The present invention relates to dispensers for caulking, sealants and the like, and more particularly to such devices providing pressure relief at the end of a dispensing cycle for avoiding spurious discharge.
Caulking guns for paste or plastic media that is typically supplied in disposable cylindrical cartridges are well known, being disclosed, for example, in U.S. Pat. No. 4,081,112 to Chang. A plunger shaft of the gun is extendable into a cartridge that is removably supported by the gun, the shaft being driven by reciprocally operating a handle mechanism for controllably dispensing the media from a nozzle of the cartridge. The drive is generally unidirectional, and principal variations of the prior art relate to operation during and following return strokes of the handle mechanism, when the plunger shaft is not being advanced.
The Chang patent discloses a gun having a drive grip that during forward movement thereof frictionally engages and forwardly drives the shaft, and a second grip that frictionally engages and holds the shaft against rearward movement, the grips being separately biased toward a gripping orientation relative to the shaft, the drive grip being upset from the gripping orientation when the handle mechanism is returned to a rest position. When it is desired to retract the plunger shaft, such as for replacing the cartridge, the second grip is manually upset from its gripping orientation. In many situations, substantial unwanted quantities of the media continue to flow from the nozzle after operation of the handle mechanism has terminated, due to swelling of the cartridge and/or deformation of the gun under high pressures needed to dispense viscous media. Such pressure can be released at least in part by releasing the second grip. However, undesirable dripping still occurs in many cases, even when a concerted effort is made to release the second grip immediately following a dispensing stroke of the handle mechanism. This is especially true at high dispensing pressures, not only because greater effort being applied to the handle mechanism cannot be as quickly terminated, but also higher forces required to release the second grip which cannot be as quickly applied as when lower pressures are involved.
Simpler dripless caulking guns not having the second grip are known. However, the complete absence of restraint during and after the return stroke is usually undesirable because there is interruption of the dispensing in each return stroke. Further, when high dispensing pressures are needed, backward motion of the plunger shaft during the return stroke can approach the distance that the shaft can be advanced in the drive stroke, thereby rendering the gun ineffective for use at high pressures. Guns for use at moderate pressures and having limited frictional restraints against rearward movement of the plunger shaft are disclosed, for example, in U.S. Pat. Nos. 4,461,407 to D. Finnigan, 4,572,409 to G. Finnigan, and 4,923,096 to Ennis. U.S. Pat. No. 4,009,804 to Costa discloses an anti-drip caulking device wherein the second grip has a spring biased, movably connected fulcrum that moves rearwardly during the return stroke of the handle mechanism for permitting a corresponding rearward movement of the plunger shaft to release pressure from the cartridge. Each of these devices of the prior art are yet subject to one or more of the following disadvantages:
1. They cannot effectively feed highly viscous media due to excessive lost motion during the backstroke; PA1 2. They cannot provide substantially continuous flow during multiple strokes of the handle mechanism, particularly at medium and high media viscosities; PA1 3. They are subject to spurious dispensing, particularly at low media viscosities; and PA1 4. They are subject to performance degradations due to ageing and/or contamination of elastomer materials used therein.
Thus there is a need for a caulking gun that is effective over a wide range of media viscosities, that can deliver a substantially continuous stream during multiple cycles of the handle mechanism, is inexpensive to provide and easy to use while offering close control without spurious dispensing.